There was some info related to this up towards the beginning of the thread. Basically, my understanding is that the chassis is going to come set up for the polymer mdt mags but steel AICS mags aren't going to latch. I can attest to this, it's true because i ran into this on a howa oryx I'm reviewing, also in 6mm CM. You have to modify the latch by filing or machining off 1mm from the top of the catch. At that point you can run steel AICS mags to get the longer COAL but cant go back to the MDT ones. The MDT mags have an insanely short COAL anyway, basically just big enough for factory loaded ammo. Hope this helps.